This invention relates to accessory casings in general and, in particular, to a new and useful valve casing and method of manufacturing said valve casing.
The manufacture of gate valve casings having large nominal widths, for example of 200 mm to 800 mm, by connecting two casing parts to each other by a longitudinal, fluid-tight weld is known. In this prior art design, each of the casing parts is provided with an outwardly projecting flange-like rim to which a pipe connection is welded. In the interior of the casing, a pipe connection is welded to each of the rimmed-out portions, with the two pipe connection ends facing each other, to which valve seat rings may be welded, forming guides and the valve seat for a shutoff member and, in the case under consideration, a gate.
Such a prior art gate valve casing has the disadvantage that the inside pipe connections providing the valve seat faces are secured by welds which cannot be inspected ultrasonically or radiographically. Such gate valve casings are, therefore, unusable in instances where particular safety regulations are to be met, for example, in nuclear power plants. In addition, gate valve casings manufactured in accordance with the prior art method, particularly large gate valves, may be very expensive. (See German Auslegungschrift Nos. 2,164,929; 1,425,710; 2,032,132 and 2,354,246; German Utility Model No. 7,031,192; German Pat. Nos. 1,928,585; 1,000,652; 755,989 and 973,519; German Offenlegungschrift Nos. 1,928,686; 2,057,746; 2,041,333 and 2,114,068; published Patent Application No. S, 28,115,X11/47 g, "Welding and Iron Materials" by Ludwig Zeyen and Wilhem Lohmann, Second Edition, 1948, published by Stahleisen mbH, Dusseldorft, page 297; "Progress in the Technology of Fittings, Particularly with Regard to Quality Inspection", by W. Kranert, 3R International, Volume 15, No. 9, September 1976, pages 530 to 535; and "Manual of the Welding Practice", Paul Schimpe and Hans A. Horn, Third Edition, Springer Publishers, 1943, Berlin, pages 173/180.)